A software-defined data center (SDDC) is a data center where information technology infrastructure is virtualized and delivered as a service. The SDDC may be fully controlled by software, meaning that the hardware configuration of each element of the SDDC is accomplished through a common software system. This is in contrast to traditional data centers where hardware devices that define the infrastructure are individually configured.
An SDDC may include an SDN overlay (hereafter interchangeably “SDN” or “overlay”). An SDN is a logical network formed and operated using logical representations of underlying physical networking components. The physical networking components are abstracted into corresponding logical or virtual representations, and the abstractions are used to define the SDN. As an example, a logical representation of a hypervisor can participate in an SDN, such that a function attributed to the logical representation of the hypervisor in the SDN is actually performed by the underlying hypervisor component in the underlay. Similarly, a logical representation of a networking gateway can participate in an SDN, such that a function attributed to the logical representation of the networking gateway in the SDN is actually performed by the underlying networking gateway component in the physical network, also called an underlay.
In an SDN, because the actual networking components that perform the networking functions are abstracted into logical entities representing the networking functionality offered by those components and not the actual implementations of those functionalities, something is needed to direct those networking functionalities into a functioning logical network. That direction is performed by an SDN controller. SDN controllers are based on protocols, such as OpenFlow, that allow servers to tell switches where to send packets.